1. Field of the Invention
The present invention generally relates to a power assist drive/steer attachment for use on a folding wheelchair to convert the wheelchair into a motor-powered chair. The invention more particularly relates to an electric or fuel drive attachment for use on a wheelchair for persons having less than full use of their legs and which is steerable. In cases where the operator possesses sufficient motor capabilities, the invention may be easily attached by the operator while seated in the chair or from an external position.
2. Description of the Related Art
Power-driven wheelchairs are known and generally are one of three types. The first type of wheelchair is an integrated "power chair" in which a motive force producing means (e.g., produced by a battery or other power source) is permanently mounted to the chair. These types of chairs include a reinforced frame and are therefore extremely heavy (e.g., typically 220 pounds or more) and expensive (e.g., approximately $5000 or more). Further, the integrated "power chair" is typically extremely bulky and cannot be folded up, thus usually requiring a relatively large vehicle (e.g., a van) with a wheelchair lift to transport such a chair when the chair is not in use. Further, the integrated "power chair" typically is unable to be manually driven. Thus, if the motive force producing means is defective or non-operational, the user is unable to transport himself/herself at all by using the chair.
A second type of power-driven wheelchair is a standard folding-type chair with an auxiliary drive unit, typically electric-powered. This type of chair is much less expensive than the integrated "power chair", is foldable (if the drive unit can be-removed) and is relatively lightweight (e.g., typically less than 80 pounds), and in some cases can be manually driven by the operator with the aid of hand rims concentric with rear wheels of the wheelchair.
A third type of power-driven wheelchair recently placed on the market is a combination of the first two types of chairs. It is power-driven (usually electric), but it can be folded up for transportation. This is accomplished by removing the power supply and in some cases the drive unit when folding is required. These chairs do not have a reinforced frame and are therefore comparable in weight with auxiliary drive chairs. Many are available for about $4000 (still expensive relative to an add-on unit). However, there are many drawbacks to these new power chairs and the conventional auxiliary drive units.
The conventional auxiliary drive units and the foldable power-driven wheelchairs are of various designs, and depending on the design, there are various problems which greatly limit performance. Of the power assist devices, many cannot be used to power the wheelchair over or onto obstacles such as over curbs or to descend from the pavement to a road in a controlled manner (i.e., as opposed to dropping thereto). Further, several of the available conventional power attachment units do not allow for steering of the wheelchair and are typically inaccessible to the operator seated in the wheelchair.
Additional problems presented by some of the conventional drive units and the foldable power chair include the lack of provisions for an operator to conveniently attach and detach the power unit and device (the requirement of an assistant in many cases), dangerous positioning of moveable parts which may injure body parts or damage clothes, inability to switch between manual and power modes, and application such that overall wheelchair stability is decreased.
There is a need for manual wheelchair users to have occasional access to a power-driven wheelchair. This is because operating a manually-driven wheelchair requires continuous activity of the user's arms and hands with substantial muscle exertion, and thus the physical effort to power such chairs is great and significantly limits the operator's mobility and endurance.
An example of a conventional power assist device is disclosed, for example, in U.S. Pat. No. 5,016,720 to Coker, in which a detachable electric drive unit for a collapsible wheelchair has a drive unit which is battery-powered. The drive unit is steerable via a steering column, which is rotatable around its vertical axis by pushing on a handlebar, and the drive unit is mounted between the user's legs in front of the wheelchair. However, such a power assist attachment has several problems.
First, the drive unit trails beneath a sling seat of the wheelchair. Thus, while the unit includes portions which are attached to the front of the wheelchair, the attachment must also be coupled to an X-shaped brace underneath the seat. This makes it extremely difficult, if not impossible, for the operator to easily and efficiently attach, detach, and access the drive unit. It also precludes the possibility of folding the chair with the unit mounted. Further, the steering column is connected by a linkage to a drive wheel, rather than directly. This configuration makes for a complex steering mechanism and precludes the possibility of 360-degree rotation of the drive wheel.
Additionally, the drive wheel is not reliably positioned or located as it traverses a straight line or in a straight direction since it is not guided by any type of mechanism. As a result, the operator must exert continuous control and pressure on the steering column to ensure that the wheelchair travels in the intended direction. This constant vigilance and control of the steering column is tedious and easily tires the operator. It is also the only drive mode available while the unit is attached. Them is no provision for switching into a manual driving mode with the device in place. Further, a flat spring provides suspension by supporting an entire fork, and ground clearance is minimal due to possible interference with low slung frame members and a fender.
Another conventional wheelchair attachment is disclosed, for example, in U.S. Pat. No. 5,113,959 to Mastov, in which a rear-mounted electric drive attachment for a wheelchair includes an electric motor and a wheel, coupled to the electric motor, for driving the wheelchair by frictionally contacting the ground. A bracket arrangement allows the wheel to be inclined to a plurality of different positions to allow the chair to negotiate curbs and obstacles; however, the advocated practice of having the operator perform a "wheelie" with the chair to climb curbs is potentially very dangerous.
This conventional design also suffers from other various drawbacks. For example, the attachment is not designed to be removed once fitted to the chair. There is no spring or other device to produce down force on the drive wheel to maintain traction, just gravity. Furthermore, there is no steering capability of the chair with the attachment.
In view of the foregoing, the conventional attachment systems have a plurality of drawbacks which make them difficult for attachment and use by the operator of the wheelchair, and preclude their attachment by an operator while seated in the chair.